Fluid pressure detection device

ABSTRACT

A fluid pressure detection device capable of accurately detecting a pressure change of a fluid flowing inside a tube includes a substrate, a piezoelectric element formed on the top surface of the substrate, a support body which is annular and surrounds the piezoelectric element and supports the top surface of the substrate, and a lid body which is provided to close the top opening of the support body, and deforms the tube with the bottom surface of the substrate by pressing the substrate through the support body.

TECHNICAL FIELD

The present invention relates to a fluid pressure detection device whichdetects pressure of a fluid flowing inside a tube.

BACKGROUND ART

For example, the heart is a pump in life which circulates bloodthroughout a whole body when four parts called “right atrium”, “rightventricle”, “left atrium” and “left ventricle” move at the same time.When these parts are moving regularly with a constant rhythm, it can besaid that normal “beating” is going on. A word “pulsation” and not“beating” is used for what passes through the inside of a tube such as ablood vessel or piping, and pulsation occurs in the case of a positivedisplacement reciprocating pump. The pulse waveform is the waveform ofartery inner pressure, and there is proposed a method of detecting thiswaveform of inner pressure from a body surface by using a piezoelectricceramic or piezoelectric polymer resin.

The Patent Document 1 below relates to a broadband sensor and disclosesconstitution that the sensor comprises an insulating substrate, apiezoelectric element mounted to the surface of the insulating substrateand a cylindrical member installed to surround the piezoelectricelement. By bringing an opening on a side opposite to the insulatingsubstrate of the cylindrical member into contact with a body surface toform an airtight cavity in the inside of the cylindrical member, a pulsewave transmitted from a blood vessel below the body surface is detectedas a change in air pressure in the cavity with the piezoelectricelement.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Patent No. 5899308

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the broadband sensor of the Patent Document 1, since the output ofthe piezoelectric element changes according to the airtightness of thecavity formed by the insulating substrate, the body surface and thecylindrical member, it is difficult to enhance the accuracy of apressure change.

It is an object of the present invention which was made in view of thissituation to provide a fluid pressure detection device which canaccurately detect from outside of a tube a pressure change of a fluidflowing inside the tube.

Means for Solving the Problem

One embodiment of the present invention relates to a fluid pressuredetection device for detecting pressure of a fluid flowing inside atube. The fluid pressure detection device includes:

a substrate;

a piezoelectric element on one surface of the substrate; and

a support body for supporting the one surface of the substrate on bothsides of the piezoelectric element, wherein the tube is deformed withthe other surface of the substrate through the support body.

Another embodiment of the present invention relates to a fluid pressuredetection device for detecting pressure of a fluid flowing inside atube. The fluid pressure detection device includes:

a substrate;

a piezoelectric element on one surface of the substrate;

a support body for supporting the one surface of the substrate on bothsides of the piezoelectric element; and

a pressing member for pressing the support body from a side opposite tothe substrate to press the other surface of the substrate against thetube.

The pressing member may apply a pressure of not less than 40 mmHg from aside opposite to the substrate of the support body.

The fluid pressure detection device may include an integrating circuitwhich integrates the output of the piezoelectric element.

The support body may support the one surface of the substrate in partsalong at least two opposed sides of a first rectangle surrounding thepiezoelectric element.

The piezoelectric element may be rectangular with long sides beingsubstantially vertical to the long sides of the first rectangle.

A plurality of the piezoelectric elements may be arranged on the onesurface of the substrate along the longitudinal direction of the firstrectangle.

The substrate may have slits on both sides of each of the piezoelectricelements in the longitudinal direction of the first rectangle.

It is to be noted that any arbitrary combination of the above-describedstructural components as well as the expressions according to thepresent invention changed among a system and so forth are all effectiveas and encompassed by the present aspects.

Effect of the Invention

According to the present invention, there can be provided a fluidpressure detection device which can accurately detect from outside of atube a pressure change of a fluid flowing inside the tube.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective sectional view of a fluid pressure detectiondevice 1 according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a support body 30 in FIG. 1 .

FIG. 3 is a sectional view of the fluid pressure detection device 1.

FIG. 4 is a sectional view showing another constitution example of thefluid pressure detection device 1.

FIG. 5 is a sectional view showing still another constitution example ofthe fluid pressure detection device 1.

FIG. 6 is a sectional view of a fluid pressure detection deviceaccording to a comparative example.

FIG. 7 is a perspective view of the fluid pressure detection device 1including the constitution of signal extraction.

FIG. 8 is a sectional view of the fluid pressure detection device 1including the constitution of signal extraction.

FIG. 9 is a schematic diagram showing that the fluid pressure detectiondevice 1 is directly pressed against a tube 7.

FIG. 10 is a graph showing the relationship between the pressuredifference of a fluid 6 flowing inside the tube 7 and a sensor outputwhen the pressing force applied to the fluid pressure detection device 1against the tube 7 is set to 1N, 2N, 3N, 4N and 5N.

FIG. 11 is a circuit diagram showing an example of an I-V conversioncircuit (impedance conversion circuit) which converts the output currentof the piezoelectric element 20 of the fluid pressure detection device 1into voltage.

FIG. 12 is a diagram showing the waveform of the output voltage Vout1 ofthe circuit shown in FIG. 11 and the waveform of a direct detectionvalue Vt obtained by directly detecting the pressure of the fluid 6 withan unshown water pressure sensor.

FIG. 13 is a circuit diagram showing an example of an integratingcircuit which integrates the output current of the piezoelectric element20 of the fluid pressure detection device 1.

FIG. 14 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor when the fluid 6 flowing inside the tube 7is pulsated with a minimum pressure of 50 mmHg to a maximum pressure of170 mmHg.

FIG. 15 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor when the fluid 6 flowing inside the tube 7is pulsated with a minimum pressure of 50 mmHg to a maximum pressure of130 mmHg.

FIG. 16 is a diagram showing the waveform of the output voltage Vout2 ofthe circuit shown in FIG. 13 and the waveform of the direct detectionvalue Vt obtained by directly detecting the pressure of the fluid 6 withan unshown water pressure sensor when the fluid 6 flowing inside thetube 7 is pulsated with a minimum pressure of 50 mmHg to a maximumpressure of 130 mmHg.

FIG. 17 is a schematic diagram showing that the fluid pressure detectiondevice 1 is pressed against the tube 7 through human skin gel 7 a.

FIG. 18 is a waveform diagram of the output voltage Vout2 of the circuitshown in FIG. 13 when the fluid 6 flowing inside the tube 7 is pulsatedwith a minimum pressure of 50 mmHg to a maximum pressure of 150 mmHg ina case where the fluid pressure detection device 1 is pressed againstthe tube 7 without the human skin gel 7 a (FIG. 9 ) and in a case wherethe fluid pressure detection device 1 is pressed against the tube 7through the human skill gel 7 a (FIG. 17 ).

FIG. 19 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor when the fluid pressure detection device 1is pressed against the tube 7 without the human skin gel 7 a in a casewhere the fluid 6 flowing inside the tube 7 is pulsated with a minimumpressure of 50 mmHg to a maximum pressure of 150 mmHg.

FIG. 20 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor when the fluid pressure detection device 1is pressed against the tube 7 through the human skin gel 7 a in theabove case.

FIG. 21 is a schematic diagram showing that the fluid pressure detectiondevice 1 is pressed against the surface (skin) of a human body 5 todeform the tube 7 which is an artery in the human body 5.

FIG. 22A and FIG. 22B are schematic sectional views of a measuringinstrument used in Examples 1 to 3, wherein FIG. 22A is a schematicsectional view before measurement and FIG. 22B is a schematic sectionalview during measurement.

FIG. 23 is a table showing measurement results (peak-peak values Vpp ofoutput voltages Vout1) in Example 3.

FIG. 24 is a bar graph obtained from the table of FIG. 23 .

FIG. 25 is a diagram showing the waveform of the output voltage Vout1 ofthe I-V conversion circuit (impedance conversion circuit) of FIG. 11 andthe waveform of the output voltage Vout2 of the integrating circuit ofFIG. 13 all of which were obtained from measurement (40 mmHg) on asubject No. 8 in Example 3.

FIG. 26A and FIG. 26B are plane views of the substrate 10 and thepiezoelectric element 20 of a fluid pressure detection device accordingto Embodiment 2 of the present invention, wherein FIG. 26A is a planeview of a first constitution example and FIG. 26B is a plane view of asecond constitution example.

FIG. 27A to FIG. 27C are perspective views of a support body 30 in asecond Embodiment, wherein FIG. 27A is a perspective view of an all-sidesupport type, FIG. 27B is a perspective view of a long-side support type(recess in a short side) and FIG. 27C is a perspective view of ashort-side support type (recess in a long side).

FIG. 28 is a bar graph showing comparison between the standardizedsensitivity (mV/mmHg) of each of the fluid pressure detection devices ofthe second Embodiment and the standardized sensitivity of each of thefluid pressure detection devices of comparative examples.

FIG. 29 is a graph showing the relationship between the displacementagainst the tube 7 and sensitivity change rate in the fluid pressuredetection devices of the second Embodiment and the fluid pressuredetection devices of the comparative examples.

FIG. 30 is a graph showing the relationship between pressing force andstandardized sensitivity according to the shape of the piezoelectricelement 20 in the fluid pressure detection devices of Embodiment 2.

FIG. 31A and FIG. 31B are plane views of the substrate 10 and thepiezoelectric elements 20 of a fluid pressure detection device accordingto a third Embodiment of the present invention, wherein FIG. 31A is aplane view of a first constitution example and FIG. 31B is a plane viewof a second constitution example.

FIG. 32A and FIG. 32B are graphs showing the relationship between thedisplacement against the tube 7 and standardized sensitivity in thefluid pressure detection device of the third Embodiment, wherein FIG.32A is a graph showing the first constitution example and FIG. 32B is agraph showing the second constitution example.

FIG. 33A and FIG. 33B are graphs showing the relationship between thedisplacement of the tube 7 and sensitivity change rate in the fluidpressure detection device of the third Embodiment, wherein FIG. 33A is agraph showing the first constitution example and FIG. 33B is a graphshowing the second constitution example.

FIG. 34 is a diagram for explaining the angle deviation between thesubstrate 10 and the tube 7.

FIG. 35A and FIG. 35B are graphs showing the relationship between theangle deviation against the tube 7 and standardized sensitivity in thefluid pressure detection device of the third Embodiment, wherein FIG.35A is a graph showing the first constitution example and FIG. 35B is agraph showing the second constitution example.

FIG. 36A and FIG. 36B are graphs showing the relationship between theangle deviation against the tube 7 and sensitivity change rate in thefluid pressure detection device of the third Embodiment, wherein FIG.36A is a graph showing the first constitution example and FIG. 36B is agraph showing the second constitution example.

FIG. 37A and FIG. 37B are explanation diagrams showing that thedeviation of an angle between the substrate 10 and the tube 7 anddisplacement therebetween are combined.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. The same or equivalentconstituent parts, members, etc., shown in the drawings are designatedby the same reference numerals and will not be repeatedly described asappropriate. The embodiments are not intended to limit the invention butare mere exemplifications, and all features or combinations thereofdescribed in the embodiments do not necessarily represent the intrinsicnatures of the invention.

First Embodiment

With reference to FIG. 1 to FIG. 21 , a fluid pressure detection device1 according to a first embodiment of the present invention will bedescribed hereinunder. The fluid pressure detection device 1 is used inoil pressure gauges, water gauges and blood pressure gauges. As shown inFIG. 1 , the fluid pressure detection device 1 comprises a substrate 10(diaphragm), a piezoelectric element 20, a support body 30 and a lidbody 40. The substrate 10 is, for example, a plate-like or sheet-likesubstrate having a thickness of 10 to 200 μm and made of a metal such asstainless steel. The top surface (one surface) of the substrate 10 is asurface for mounting the piezoelectric element 20. The bottom surface(the other surface) of the substrate 10 is a surface to be pressedagainst a 7 shown in FIG. 9 . The piezoelectric element 20 is, forexample, a piezoelectric ceramic having a thickness of 10 to 200 μm andformed (mounted) on the top surface (the one surface) of the substrate10. A metal electrode (for example a gold electrode having a thicknessof several μm to 20 μm formed by gold sputtering) for taking out signalsis formed on both surfaces of the piezoelectric element 20 but not shownin FIG. 1 . The metal electrodes and the piezoelectric element 20constitute a piezoelectric unimorph. The substrate 10 and thepiezoelectric element 20 are substantially circular in the example ofFIG. 1 .

The support body 30 is a circularly annular member having a much largerthickness (height) than the piezoelectric element 20 and made of a rigidmaterial such as stainless steel. The support body 30 is provided tosurround the piezoelectric element 20. As shown in FIG. 1 and FIG. 3 ,the support body 30 has a stepped part 32 in the vicinity of the inneredge part of the bottom surface. With the stepped part 32, the supportbody 30 supports the top surface of the substrate 10 in the vicinity ofthe outer edge. As shown in FIG. 2 , the support body 30 has a notch 31at the inner edge for leading out wires.

The lid body 40 is a plate-like or sheet-like body having substantiallythe same shape as the substrate 10 in plane view and made of a metalsuch as stainless steel. The lid body 40 is mounted to the upper end(one end) of the support body 30 to close the top opening (one-endopening) of the support body 30. As shown in FIG. 7 , the lid body 40has a through hole 41 for leading out wires. The through hole 41communicates with the notch 31 of the support body 30. On the topsurface of the lid body 40, a terminal part 50 is provided. The terminalpart 50 is electrically connected to the piezoelectric element 20 bywires 51. From the terminal part 50, cables 60 extend for connecting toa circuit (FIG. 11 or FIG. 13 ) in an unshown measuring instrument.

The support of the substrate 10 with the support body 30 is not limitedto support with the stepped part 32 shown in FIG. 1 and FIG. 3 . Thesubstrate 10 may be supported by the bottom surface of the support body30 having no stepped part 32 as shown in FIG. 4 . Further, as shown inFIG. 5 , the lid body 40 may not be provided. In a comparative exampleshown in FIG. 6 , the outer edge (outer peripheral surface) of thesubstrate 10 is supported by the inner peripheral surface of the supportbody 30. But the support structures shown in FIGS. 3 to 5 are preferredfrom the viewpoint of the reproducibility of pressure detection.

FIG. 9 is a schematic diagram showing that the fluid pressure detectiondevice 1 is directly pressed against the tube 7. This schematic diagramshows the cross section of an evaluation device for quantitativelyevaluating the fluid pressure detection device 1. The tube 7 is, forexample, a silicone tube having flexibility or viscoelasticity. The tube7 is held in a tube holder 8 having a U-shaped cross section. The outerdiameter of the tube 7 is 6 mm. A fluid 6 supplied from an unshownpiston pump flows (transferred with pulsation) inside the tube 7. Whendetecting the pressure of the fluid 6, by a force gauge 9 the fluidpressure detection device 1 is pressed from the lid body 40 side (thesupport body 30 is pressed from a side opposite to the substrate 10) sothat the other surface of the substrate 10 is pressed against the tube 7to deform the tube 7. Measurement results which will be givenhereinafter were obtained when the fluid 6 was supplied at 96 bpm by thepumping function of the above piston pump. The pressure of the fluid 6was also directly detected by an unshown pressure sensor (Model AP-13Sof KEYENCE CORPORATION) to evaluate the output of the fluid pressuredetection device 1.

FIG. 10 is a graph showing the relationship between the pressuredifference of the fluid 6 flowing inside the tube 7 and the output ofthe sensor when the pressing force applied to the fluid pressuredetection device 1 against the tube 7 was set to 1N, 2N, 3N, 4N and 5N.This graph is a linear approximation graph of the peak-peak value of theoutput voltage (output voltage Vout1 of a circuit shown in FIG. 11 whichwill be described hereinafter) of the fluid pressure detection device 1for each pressing force when measurement was made by setting thepressure difference to 40 mmHg (minimum pressure of 50 mmHg to maximumpressure of 90 mmHg), 80 mmHg (minimum pressure of 50 mmHg to maximumpressure of 130 mmHg) and 120 mmHg (minimum pressure of 50 mmHg tomaximum pressure of 170 mmHg). It could be confirmed from FIG. 10 thatthe pressure difference of the fluid 6 flowing inside the tube 7 and theoutput voltage of the fluid pressure detection device 1 have highcorrelation with a correlation coefficient of more than 0.98 at anypressing force, and are substantially in proportion to each other. Thepressing force was set to 3N in the following measurement.

FIG. 11 is a circuit diagram showing an example of an I-V conversioncircuit (impedance conversion circuit) which converts the output currentof the piezoelectric element 20 of the fluid pressure detection device 1into voltage. This circuit constitutes a closed loop with thepiezoelectric element 20 and a resistor R1, and an output voltage Vout1appears at both ends of the resistor R1. The output voltage Vout1 is inproportion to the time differential of a charge generated in thepiezoelectric element 20, that is, the pressure change rate of the fluid6, where the proportional constant is the resistance value of theresistor R1. FIG. 12 is a waveform diagram showing the waveform of theoutput voltage Vout1 of the circuit shown in FIG. 11 and the waveform ofa direct detection value Vt obtained by directly detecting the pressureof the fluid 6 with an unshown water pressure sensor. It could beconfirmed from FIG. 12 that the output voltage Vout1 is linked with theinclination of the direct detection value Vt. The difference in thefluid pressure (maximum pressure−minimum pressure) produced by thebeating of a piston pump can be detected by the circuit shown in FIG. 11.

FIG. 13 is a circuit diagram showing an example of an integratingcircuit which integrates the output current of the piezoelectric element20 of the fluid pressure detection device 1. This circuit is anintegrating circuit utilizing an operation amplifier A1 and accumulatesthe output current of the piezoelectric element 20 in a capacitor C1provided between the output terminal and the inverted input terminal ofthe operation amplifier A1. One end of the piezoelectric element 20 isconnected to the ground as a fixed voltage terminal. The other end ofthe piezoelectric element 20 is connected to one end of a resistor R2.The other end of the resistor R2 is connected to the inverted inputterminal of the operation amplifier A1. The non-inverted input terminalof the operation amplifier A1 is connected to the ground. The capacitorC1 and a resistor R3 are connected in parallel to each other between theoutput terminal and the inverted input terminal of the operationamplifier A1. The resistor R3 is provided to prevent the saturation ofthe output of the operation amplifier A1. The operation amplifier A1 isdriven by two power sources and connected to a positive side power line(voltage Vcc) and to a negative side power line (voltage −Vcc). Sincethe inverted input terminal voltage of the operation amplifier A1becomes substantially equal to ground potential by a virtual short, anoutput voltage Vout2 which appears at the output terminal of theoperation amplifier A1 is voltage between both ends of the capacitor C1.The output voltage Vout2 is in proportion to the integral of the outputcurrent of the piezoelectric element 20 where the proportional constantis the reciprocal of the capacitance value of the capacitor C1. Theoriginal charge generation output waveform of the piezoelectric element20 is obtained by the circuit shown in FIG. 13 , thereby making itpossible to calculate a pressure change.

FIG. 14 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor when the fluid 6 flowing inside the tube 7is pulsated with a minimum pressure of 50 mmHg to a maximum pressure of170 mmHg. Results shown in FIG. 14 were obtained by measuring for 10seconds at a sampling frequency of 1 kHz and the number of data pieceswas 10,000. These conditions are the same as in the correlation graphsshown in FIG. 15 , FIG. 19 and FIG. 20 . It could be confirmed from FIG.14 that the output voltage Vout2 and the direct detection value Vt havehigh correlation with a correlation coefficient of more than 0.99.Therefore, the difference between the minimum pressure and the maximumpressure of the fluid 6 flowing inside the tube 7 can be detected fromthe peak-peak value of the output voltage Vout2.

FIG. 15 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor in cases where the fluid 6 flowing insidethe tube 7 is pulsated with a minimum pressure of 50 mmHg to a maximumpressure of 130 mmHg. FIG. 16 is a diagram showing the waveform of theoutput voltage Vout2 of the circuit shown in FIG. 13 and the waveform ofthe direct detection value Vt obtained by directly detecting thepressure of the fluid 6 with an unshown water pressure sensor in theabove case. It could be confirmed from FIG. 15 that the output voltageVout2 and the direct detection value Vt have high correlation as in FIG.14 . Also, it could be confirmed from FIG. 16 that the waveform of theoutput voltage Vout2 and the waveform of the direct detection value Vtare almost the same.

FIG. 17 is a schematic diagram showing that the fluid pressure detectiondevice 1 is pressed against the tube 7 through human skin gel 7 a. Thisschematic diagram shows the cross section of an evaluation device forquantitatively evaluates the fluid pressure detection device 1. FIG. 17differs from FIG. 9 in that the human skin gel 7 a having flexibility orviscoelasticity is added, but is the same in other points. By adding thehuman skin gel 7 a, a state is made close to the pressure measurement(blood pressure measurement) of a blood flowing inside a blood vessel ofa human body.

FIG. 18 is a waveform diagram of the output voltage Vout2 of the circuitshown in FIG. 13 when the fluid 6 flowing inside the tube 7 is pulsatedwith a minimum pressure of 50 mmHg to a maximum pressure of 150 mmHg ina case where the fluid pressure detection device 1 is pressed againstthe tube 7 without the human skin gel 7 a (FIG. 9 ) and in a case wherethe fluid pressure detection device 1 is pressed against the tube 7through the human skin gel 7 a (FIG. 17 ). It could be confirmed fromFIG. 18 that though sensitivity (amplitude) drops, almost the samewaveform is obtained between when the fluid pressure detection device 1is pressed through the human skin gel 7 a against the tube 7 and when itis pressed not through the human skin gel 7 a against the tube 7.

FIG. 19 is a diagram showing correlation between the output voltageVout2 of the circuit shown in FIG. 13 and the direct detection value Vtobtained by directly detecting the pressure of the fluid 6 with anunshown water pressure sensor when the fluid pressure detection device 1is pressed against the tube 7 without the human skin gel 7 a in a casewhere the fluid 6 flowing inside the tube 7 is pulsated with a minimumpressure of 50 mmHg to a maximum pressure of 150 mmHg. FIG. 20 is adiagram showing correlation between the output voltage Vout2 of thecircuit shown in FIG. 13 and the direct detection value Vt obtained bydirectly detecting the pressure of the fluid 6 with an unshown waterpressure sensor when the fluid pressure detection device 1 is pressedagainst the tube 7 through the human skin gel 7 a in the above case. Inthe measurement which is the basis of the results of FIG. 20 , the humanskin gel (Model H0-2) of EXSEAL CORPORATION was used as the human skingel 7 a. It could be confirmed from comparison between FIG. 19 and FIG.20 that when the fluid pressure detection device 1 is pressed againstthe tube 7 through the human skin gel 7 a, the output voltage Vout2 andthe direct detection value Vt have high correlation with a correlationcoefficient of more than 0.97, though the correlation coefficientslightly drops compared with the case where the fluid pressure detectiondevice 1 is pressed against the tube 7 without the human skin gel 7 a.

FIG. 21 is a schematic diagram showing that the fluid pressure detectiondevice 1 is pressed against the surface (skin) of a human body 5 todeform the tube 7 which is an artery in the human body 5. A pressingmember 70 is used to press the bottom surface of the substrate 10against the tube 7 by pressing the support body 30 from a side oppositeto the substrate 10. The pressing member 70 may be just a belt or anadhesive tape such as an adhesive bandage having a viscous surface. Bypressing the bottom surface of the substrate 10 against the tube 7through the support body 30 to deform the tube 7 as shown in FIG. 21 ,the difference between the minimum pressure (minimum blood pressure) andthe maximum pressure (maximum blood pressure) of the fluid 6 (blood)flowing inside the tube 7 can be detected from outside the human body 5more accurately than before. The existence of the support body 30 makesit possible to carry out stable detection with excellentreproducibility.

Example 1

FIG. 22A and FIG. 22B are schematic sectional views of a measuringinstrument used in Examples 1 to 3. FIG. 22A is of before measurement.FIG. 22B is of during measurement. This measuring instrument was made bycombining a frame body 81, a round wire coil spring 82 and a cap 83 withthe fluid pressure detection device 1 of FIG. 7 whose support body 30having an outer diameter of 12 mm. The frame body 81 is provided toguide the pressing of the cap 83 and hold the pressed cap 83. The roundwire coil spring 82 has an outer diameter of 8 mm, a total length of 15mm and a spring constant of 0.1 N/mm. The cap 83 is made of polyurethaneand has an outer diameter of 18 mm and an inner diameter of 14 mm. Thespot facing depth “a” of the cap 83, the thickness “b” of the fluidpressure detection device 1 and the total length (natural length) of theround wire coil spring 82 were set to ensure that a pressure of 40 mmHgshould be applied to the top surface of the fluid pressure detectiondevice 1 by the round wire coil spring 82 when the cap 83 was pressed tothe lower limit position as shown in FIG. 22B.

The above measuring instrument was fixed to the skin (position at whicha pulse can be felt) above the superficial temporal artery of each ofeight subjects by using the surgical tape of 3M Company while the roundwire coil spring 82 was compressed as shown in FIG. 22B, and the outputvoltage Vout1 of the I-V conversion circuit (impedance conversioncircuit) of FIG. 11 was measured. As a result, stable output wasobtained in all the subjects. Therefore, it was found that, when apressure of 40 mmHg is applied to the top surface of the fluid pressuredetection device 1, normal blood pressure measurement is possible abovethe superficial temporal artery.

Example 2

The same measurement as in Example 1 was made on the common carotidartery of each of eight subjects. That is, the above measuringinstrument was fixed to the skin (position at which a pulse can be felt)above the common carotid artery in the same manner as in Example 1 tomeasure the output voltage Vout1. As a result, stable output wasobtained in all the subjects. Therefore, it was found that when apressure of 40 mmHg is applied to the top surface of the fluid pressuredetection device 1, normal blood pressure measurement is possible abovethe common carotid artery.

Example 3

The same measurement as in Example 1 was made on the radial artery ofeach of eight subjects. That is, the above measuring instrument wasfixed to the skin (position at which a pulse can be felt) above theradial artery in the same manner as in Example 1 to measure the outputvoltage Vout1. In this example, three types of round wire coil springs82 were used. That is, in addition to a type used in Example 1, a roundwire coil spring 82 having an outer diameter of 8 mm, a total length of20 mm and a spring constant of 0.1 N/mm, and a round wire coil spring 82having an outer diameter of 10 mm, a total length of 15 mm and a springconstant of 0.2 N/mm were used. And then by adjusting the spot facingdepth of the cap 83, a pressure of 40 mmHg, 60 mmHg, 80 mmHg, 100 mmHgor 120 mmHg was applied to the top surface of the fluid pressuredetection device 1 to carry out the above measurement.

FIG. 23 is a table showing measurement results (peak-peak values Vpp ofoutput voltages Vout1) in Example 3. FIG. 24 is a bar graph obtainedfrom the table of FIG. 23 . The numerical values of the measurementresults are average values of the peak-peak values Vpp (maximum−minimum)of last 10 beats in a measurement time of 30 seconds. In FIG. 23 andFIG. 24 , the expression “fixing with tape” means that the fluidpressure detection device 1 is fixed with a surgical tape without usingthe frame body 81, the round wire coil spring 82 and the cap 83 toprevent its displacement, without being conscious of pressure. In thecase of “fixing with a tape”, output could not be obtained in twosubjects No. 6 and No. 8 as shown in FIG. 23 and FIG. 24 . Meanwhile,when a pressure of 40 mmHg, 60 mmHg, 80 mmHg, 100 mmHg or 120 mmHg wasapplied to the top surface of the fluid pressure detection device 1,output could be obtained in all the subjects. Therefore, it was foundthat when a pressure of 40 mmHg is applied to the top surface of thefluid pressure detection device 1, normal blood pressure measurement ispossible above the radial artery.

Although a pressure at which the highest peak-peak value Vpp wasobtained differed according to each subject, in all the subjects, ahigher peak-peak value Vpp was obtained when a 60 mmHg pressure wasapplied than when a 40 mmHg pressure was applied, and a higher peak-peakvalue Vpp was obtained when a 80 mmHg pressure was applied than when a60 mmHg pressure was applied. Further, in all the subjects exceptsubject No. 2, a higher peak-peak value Vpp was obtained when a 100 mmHgpressure was applied than when a 80 mmHg pressure was applied.Meanwhile, in all the subjects except subjects No. 5 and No. 6, a lowerpeak-peak value Vpp was obtained when a 120 mmHg pressure was appliedthan when a 100 mmHg pressure was applied. From the viewpoint of aburden on each subject, a lower pressure is more preferred. Therefore,in consideration of balance between sensitivity and a burden on subject,it was found that a pressure of not more than 100 mmHg or not more than80 mmHg is preferred.

For the measurement of blood pressure with the fluid pressure detectiondevice 1, it is not necessary to use the frame body 81, the round wirecoil spring 82 and the cap 83 as in the above measurement instrument. Toobtain a required pressure, an elastic body such as rubber may be placedon the fluid pressure detection device 1, and the fluid pressuredetection device 1 may be fixed on a measurement point with a surgicaltape from above the elastic body. Alternatively, the fluid pressuredetection device 1 may be fixed on a measurement point with an elastictape stretched by a predetermined length. At this point, a spacer (suchas a pad) may be placed on the fluid pressure detection device 1 toobtain a required thickness. The fluid pressure detection device 1 andmembers for fixing it on the measurement point may be as a wholeconsidered as a fluid pressure detection device.

FIG. 25 is a diagram showing the waveform of the output voltage Vout1 ofthe I-V conversion circuit (impedance conversion circuit) of FIG. 11 andthe waveform of the output voltage Vout2 of the integrating circuit ofFIG. 13 both of which were obtained from measurement (40 mmHg) on asubject No. 8 in Example 3. It could be confirmed from FIG. 25 thatwaveforms having little noise were obtained.

Second Embodiment

FIG. 26A and FIG. 26B are plane views of the substrate 10 and thepiezoelectric element 20 of a fluid pressure detection device accordingto a second Embodiment of the present invention. FIG. 26A shows a firstconstitution example and FIG. 26B shows a second constitution example.The fluid pressure detection device of this embodiment differs from thefluid pressure detection device of a first embodiment in that thesubstrate 10 and the piezoelectric element 20 are substantiallyrectangular and the support body 30 is rectangularly annular like theouter shape of the substrate 10, but is the same in other points. Forthe detection of the pressure of the fluid 6, the longitudinal directionof the substrate 10 and the extending direction of the tube 7 are madeparallel to each other. In the first constitution example shown in FIG.26A, the long sides of the piezoelectric element 20 are substantiallyvertical to the long sides of the substrate 10 (substantially parallelto the short sides). In the second constitution example shown in FIG.26B, the long sides of the piezoelectric element 20 are substantiallyparallel to the long sides of the substrate 10. When the support body 30is of an all-side support type shown in FIG. 27A, it supports all thesides (four sides) and therearound of the substrate 10. When the supportbody 30 is of a long-side support type (having a recessed part 33 in alower part of a short side) shown in FIG. 27B, it supports two longsides and therearound of the substrate 10 (no contact with a shortside). When the support body 30 is of a short-side support type (havinga recessed part 34 in a lower part of a long side) shown in FIG. 27C, itsupports two short sides and therearound of the substrate 10 (no contactwith a long side). In the following description, the support body 30 isof the all-side support type shown in FIG. 27A.

FIG. 28 is a bar graph showing comparison between the standardizedsensitivity (mV/mmHg) of each of the fluid pressure detection devices ofthe second Embodiment and the standardized sensitivity of each of thefluid pressure detection devices of comparative examples. The term“standardized sensitivity” is obtained by dividing the peak-peak valueof the output voltage Vout1 of the circuit shown in FIG. 11 by adifference between the minimum pressure and the maximum pressure andbased on an actual measurement value. In FIG. 28 , #1 represents acomparative example in which the substrate 10 is circular with adiameter of 9 mm, the support body 30 is circularly annular and thepiezoelectric element 20 has the same shape as that of the firstconstitution example of this embodiment. #2 represents the firstconstitution example of this embodiment in which the size of substrate10 is 8 mm×18 mm. #3 represents a comparative example in which thesubstrate 10 is circular with a diameter of 9 mm, the support body 30 iscircularly annular and the piezoelectric element 20 has the same shapeas that of the second constitution example of this embodiment. #4represents the second constitution example of this embodiment in whichthe size of the substrate 10 is 8 mm×18 mm. In all of #1 to #4, the sizeof the piezoelectric element is 2 mm×4 mm. The comparative examples arejust for the second Embodiment and not excluded from the presentinvention.

It was found from comparison between #1 and #2 that higher sensitivityis obtained with the rectangular substrate 10 than with the circularsubstrate 10 when the longitudinal direction of the piezoelectricelement 20 is parallel to the short-length direction of the substrate 10even if the short sides of the rectangle are shorter than the diameterof the circle. It was also found from comparison between #3 and #4 thatthere is not so much difference in sensitivity between the circularsubstrate 10 and the rectangular substrate 10 when the longitudinaldirection of the piezoelectric element 20 is parallel to thelongitudinal direction of the substrate 10.

FIG. 29 is a graph showing the relationship between the displacementagainst the tube 7 and sensitivity change rate in the fluid pressuredetection devices of the second Embodiment and the fluid pressuredetection devices of the comparative examples. The displacement on theabscissa axis in FIG. 29 is the relative amount of displacement of thetube 7 in the short-length direction of the substrate 10 while theextending direction of the tube 7 remains parallel to the longitudinaldirection of the substrate 10. “0 mm” on the abscissa axis means thatthe tube 7 passes the center of the substrate 10 in the short-lengthdirection. It was found from FIG. 29 that when the amount ofdisplacement is not more than 2 mm, the reduction of sensitivity causedby displacement is suppressed more in #2 and #4 in which the substrate10 is rectangular than #1 and #3 in which the substrate 10 is circular.

According to this embodiment, the reduction of sensitivity caused bydisplacement can be suppressed as compared with a case where thesubstrate 10 is circular and the support body 30 is circularly annular.Therefore, even when the mounting position of the fluid pressuredetection device is limited, the reduction of sensitivity can besuppressed. When the longitudinal direction of the piezoelectric element20 is parallel to the short-length direction of the substrate 10 as inthe first constitution example, sensitivity can be further improved ascompared with a case where the substrate 10 is circular.

FIG. 30 is a graph showing the relationship between pressing force andstandardized sensitivity according to the shape of the piezoelectricelement 20 in the fluid pressure detection devices of the secondEmbodiment. #5 represents an example in which the size of thepiezoelectric element 20 is 1 mm×8 mm in the second constitution exampleof this embodiment. It was found from FIG. 30 that the standardizedsensitivity of the constitution of #2 was the highest. Therefore, in athird Embodiment which will be described hereinafter, furtherimprovement will be made based on the constitution of #2.

Third Embodiment

FIG. 31A and FIG. 31B are plane views of the substrate 10 and thepiezoelectric elements 20 of a fluid pressure detection device accordingto a third Embodiment of the present invention. FIG. 31A shows a firstconstitution example and FIG. 31B shows a second constitution example.The first constitution example of this embodiment is the same as thefirst constitution example (FIG. 26A) of the second Embodiment exceptthat three piezoelectric elements 20 are arranged (arrayed) in thelongitudinal direction of the substrate 10. The second constitutionexample of this embodiment is the same as the first constitution exampleexcept that the substrate 10 has slits 11 on both sides in theshort-length direction of each piezoelectric element 20. The slits 11are parallel to the longitudinal directions of the piezoelectricelements 20. To distinguish the three piezoelectric elements 20 from oneanother, they are represented by E1, E2 and E3 from top in the figure.The I-V conversion circuit shown in FIG. 11 and the integrating circuitshown in FIG. 13 are provided for each piezoelectric element 20.

FIG. 32A and FIG. 32B are graphs showing the relationship between thedisplacement against the tube 7 and standardized sensitivity in thefluid pressure detection device of the third Embodiment. FIG. 32A showsthe first constitution example and FIG. 32B shows the secondconstitution example. FIG. 33A and FIG. 33B are graphs showing therelationship between the displacement against the tube 7 and sensitivitychange rate in the fluid pressure detection device of the thirdEmbodiment. FIG. 33A shows the first constitution example and FIG. 33Bshows the second constitution example. It was found from comparisonbetween FIG. 32A and FIG. 32B and comparison between FIG. 33A and FIG.33B that the reduction of sensitivity caused by a displacement amount ofnot more than 2 mm is suppressed when the substrate 10 has the slits 11.

FIG. 34 is a diagram for explaining the angle deviation between thesubstrate 10 and the tube 7. The angle deviation to be studiedhereinafter is an angle at which the extending direction of the tube 7turns relative to the longitudinal direction of the substrate 10 whilethe tube 7 passes the center of the substrate 10 as shown in FIG. 34 .0° means that the extending direction of the tube 7 is parallel to thelongitudinal direction of the substrate 10.

FIG. 35A and FIG. 35B are graphs showing the relationship between theangle deviation against the tube 7 and standardized sensitivity in thefluid pressure detection device of the third Embodiment. FIG. 35A showsthe first constitution example and FIG. 35B shows the secondconstitution example. FIG. 36A and FIG. 36B are graphs showing therelationship between the angle deviation against the tube 7 andsensitivity change rate in the fluid pressure detection device of thethird Embodiment. FIG. 36A shows the first constitution example and FIG.36B shows the second constitution example. As shown in the graphs, itwas found that, even when an angle deviation occurs, the centralpiezoelectric element 20 can maintain a high sensitivity of not lessthan 80% as compared with a case where there is no angle deviation. Whena certain amount of displacement is added to an angle deviation as shownin FIG. 37A and FIG. 37B, one of the piezoelectric elements 20 exceptthe central piezoelectric element 20 can maintain high sensitivity.Stated more specifically, in the case of FIG. 37A, a lower piezoelectricelement 20 in the figure maintains high sensitivity. In the case of FIG.37B, an upper piezoelectric element 20 in the figure maintains highsensitivity.

According to this embodiment, the reduction of sensitivity caused by theangle deviation (and a combination of angle deviation and displacement)of the tube 7 can be suppressed by arraying the piezoelectric elements20. Also, the reduction of sensitivity caused by the displacement of thetube 7 can be suppressed by forming the slits 11 as in the secondconstitution example. The number of the piezoelectric elements 20 is notlimited to three and may be 2, or 4 or more. The piezoelectric elements20 may be arranged in a matrix in the longitudinal direction andshort-length direction of the substrate 10 or in two arbitrarydirections of the substrate 10.

While the invention has been described in its preferred embodiments, itis to be understood by a person having ordinary skill in the art thatvariations may be made on each constituent element and process of theembodiments without departing from the scope of the following claims.Variations of the invention will be described hereinafter.

The substrate 10, the support body 30 and the lid body 40 may beinsulators made of a resin or the like. The support body 30 is notlimited to a single annular member. A plurality of support bodies 30 maybe provided on both sides of or around the piezoelectric elements 20.Specific numerical values (sizes of the substrate 10 and thepiezoelectric elements 20, pressing force, etc.) shown in aboveembodiments are just examples and may be suitably changed according torequired specifications.

EXPLANATIONS OF LETTERS OF NUMERALS

1 fluid pressure detection device, 5 human body, 6 fluid, 7 tube, 7 ahuman skin gel, 8 tube holder, 9 force gauge, 10 substrate (diaphragm),11 slit, 20 piezoelectric element, 30 support body, 31 notch, 32 steppedpart, 33, 34 recessed part, 40 lid body, 41 through hole, 50 terminalpart, 60 cable, 70 pressing member, 81 frame body, 82 round wire coilspring, 83 cap.

The invention claimed is:
 1. A fluid pressure detection device fordetecting pressure of a fluid flowing inside a tube, comprising: asubstantially rectangular substrate having first and second surfaces andlonger sides and shorter sides; a piezoelectric element on the firstsurface of the substrate; the piezoelectric element is rectangular inshape and has longer sides and shorter sides; and a support body forsupporting the first surface of the substrate on opposing sides of thepiezoelectric element, wherein the tube is deformed with the secondsurface of the substrate through the support body, wherein the supportbody is a rectangular ring having a rectangular ring opening which formsa first rectangle surrounding the piezoelectric element, the supportbody supports the first surface of the substrate in parts along at leasttwo opposed sides of the first rectangle, and the longer sides of thepiezoelectric element are substantially perpendicular to longer sides ofthe first rectangle.
 2. The fluid pressure detection device according toclaim 1, comprising an integrating circuit which integrates anelectrical signal output by the piezoelectric element.
 3. The fluidpressure detection device according to claim 1, including a plurality ofthe piezoelectric elements arranged on the first surface of thesubstrate along a longitudinal direction of the first rectangle.
 4. Thefluid pressure detection device according to claim 3, wherein thesubstrate has slits on opposing sides of each of the piezoelectricelements in the longitudinal direction of the first rectangle.
 5. Afluid pressure detection device for detecting pressure of a fluidflowing inside a tube, comprising a substantially rectangular substratehaving first and second surfaces and longer side and shorter sides; apiezoelectric element on the first surface of the substrate; thepiezoelectric element is rectangular in shape and has longer sides andshorter sides; a support body for supporting the first surface of thesubstrate on opposing sides of the piezoelectric element; and a pressingmember for pressing the support body from a side opposite to thesubstrate to press the second surface of the substrate against the tube,wherein the support body is a rectangular ring having a rectangular ringopening which forms a first rectangle surrounding the piezoelectricelement, the support body supports the first surface of the substrate inparts along at least two opposed sides of the first rectangle, and thelonger sides of the piezoelectric element are substantiallyperpendicular to longer sides of the first rectangle.
 6. The fluidpressure detection device according to claim 5, wherein the pressingmember applies a pressure of not less than 40 mmHg from a side oppositeto the substrate of the support body.
 7. The fluid pressure detectiondevice according to claim 5, comprising an integrating circuit whichintegrates an electrical signal output by the piezoelectric element. 8.The fluid pressure detection device according to claim 5, including aplurality of the piezoelectric elements arranged on the first surface ofthe substrate along a longitudinal direction of the first rectangle. 9.The fluid pressure detection device according to claim 8, wherein thesubstrate has slits on opposing sides of each of the piezoelectricelements in the longitudinal direction of the first rectangle.